Warn when the user provides volume mounts with sensitive targets when building images

[scottfrederick]

Users can provide optional bindings in the Maven spring-boot:build-image and Gradle bootBuildImage configuration. There are a few directories that are used by buildpacks during the image building process, and using these directories as the container destination path of a binding can cause problems that are difficult to diagnose. These directories include /cnb, /layers, and /workspace (or c:\cnb, c:\layers, and c:\workspace when building on Windows).

The plugins should warn the user if any of these directories is used as the destination path in a binding.